In pre-ceramic monomer formulations for the fabrication of polymer waveguides and three-dimensional interconnected structures, monomer formulations enable polymer waveguide formation and direct conversion to interconnected three-dimensional ceramics.
Currently, polymer cellular materials that are mass produced are created through various foaming processes, which all yield random (not ordered) 3D microstructures. An ordered three-dimensional (3D) microstructure is an ordered 3D structure at the micrometer or nanometer scale. Techniques do exist to create polymer materials with ordered 3D microstructures, such as stereolithography techniques; however, these techniques rely on a bottom-up, layer-by-layer approach which prohibits scalability.
A stereolithography technique provides a method to build a 3D microstructure in a layer-by-layer process. This process usually involves a platform (e.g., substrate) that is lowered into a photo-monomer bath in discrete steps. At each layer, a laser is used to scan over the area of the photo-monomer that is to be cured (i.e., polymerized) for that particular layer. Once the layer is cured, the platform is lowered by a specific amount (i.e., determined by the processing parameters and desired feature/surface resolution), and the process is repeated until the complete 3D structure is created. One example of such a stereolithography technique is disclosed in Hull et al., APPARATUS FOR PRODUCTION OF THREE-DIMENSIONAL OBJECTS BY STEREOLITHOGRAPHY, U.S. Pat. No. 4,575,330, Mar. 11, 1986, which is incorporated by reference herein in its entirety.
Modifications to the above described stereolithography technique have been developed to improve the resolution by using laser optics and special resin formulations, as well as modifications to decrease the fabrication time of the 3D structure by using a dynamic pattern generator to cure an entire layer at once. One example of such a modification is disclosed in Bertsch et al., “Microstereolithography: A Review,” Materials Research Society Symposium Proceedings, Vol. 758, 2003, which is incorporated by reference herein in its entirety. A fairly recent advancement to the standard stereolithography technique includes a two-photon polymerization process as disclosed in Sun et al., “Two-Photon Polymerization And 3D Lithographic Microfabrication,” APS, Vol. 170, 2004, which is incorporated by reference herein in its entirety. However, this advance process still relies on a complicated and time consuming layer-by-layer approach.
3D ordered polymer cellular structures have also been created using optical interference pattern techniques, also called holographic lithography; however, structures made using these techniques have an ordered structure at the nanometer scale and the structures are limited to the possible interference patterns, as described in Campbell et al., “Fabrication Of Photonic Crystals For The Visible Spectrum By Holographic Lithography,” NATURE, Vol. 404, Mar. 2, 2000, which is incorporated by reference herein in its entirety.
Previous works have also been done on creating polymer optical waveguides. A polymer optical waveguide can be formed in certain photopolymers that undergo a refractive index change during the polymerization process. When a monomer that is photo-sensitive is exposed to light (e.g., UV light) under the right conditions, the initial area of polymerization, such as a small circular area, will “trap” the light and guide it to the tip of the polymerized region due to the index of refraction change, further advancing that polymerized region. If the polymer is sufficiently transparent to the wavelength of light used to initiate polymerization, this process will continue, leading to the formation of a waveguide structure, or fiber, with approximately the same cross-sectional dimensions along its entire length. This phenomenon has been suggested for applications such as fiber optic interconnects. The existing techniques to create polymer optical waveguides have only allowed one or a few waveguides to be formed, and these techniques have not been used to create a self-supporting three-dimensional structure by patterning polymer optical waveguides.
Recently, there has been interest in using inorganic polymer materials, such as pre-ceramic polymers to form ceramic micro-truss structures. Advantages of ceramic micro-truss materials includes high temperature stability and attractive strength to weight ratios. The importance of these high temperature ceramic micro-truss structures makes these structures amenable to a wide variety of applications, such as the automotive and aerospace industries. These ceramic micro-truss materials could be used for lightweight, high temperature structural applications or for other applications that can utilize the unique porosity, such as thermal ground planes.
Typically, these pre-ceramic polymers generally contain silicon (Si) in the molecular backbone and can be converted to a ceramic material. There are a wide variety of known pre-ceramic polymers. Examples include Starfire RD-633, Starfire SMP-10, Starfire SOC-A35, Clariant/KiON Ceraset 20 (polysilazanes), polycarbosilanes, silicone resins, polysilanes, polyvinylborazine, polyborazylene, borasine-modified hydridopolysilazanes and decaborane based polymers. These pre-ceramic polymers have been used to form specific polymer-based structures that can be subsequently heat treated (pyrolyzed/sintered) to create near net shape ceramic structures.
Other ceramic micro-truss structures have been made using the original polymer micro-truss structure (or a carbon/graphite micro-truss structure that originates from the original micro-truss structure) as a template. Typically, these techniques rely on gas-phase or dip coating processes to create a ceramic micro-truss structure.
Therefore, while these aforementioned ceramic structures can be useful, they are often disadvantageously time consuming to make, using pyrolysis, sintering, gas-phase or dip coating processes, which can often require additional steps. Also, ceramic structures, such as foams, are not ordered microstructures and can suffer from random interconnections in their forms, thereby reducing the strength of the materials.
Thus, there exists a need for creating lower cost ceramic micro-truss structures with pre-ceramic monomer and polymers, which allow direct conversion to a ceramic micro-truss without the need of any additive materials. Further, it would be advantageous to provide monomer and polymer formulations that would enable polymer waveguide formation and direct conversion to these interconnected three-dimensional ceramics. Accordingly, it would be advantageous to provide pre-ceramic monomer and polymer formulations that can be used to create polymer waveguides and interconnected three-dimensional ceramic structures that are lightweight, highly durable, hard materials, and can withstand a high temperature oxidizing environment.